Abstract:The thermal decomposition process of (NH₄)₃AlF₆ was studied by DTA-TGA method and the related thermodynamic data were obtained. The results show that AlF₃ is obtained after three-step decomposition reaction of (NH₄)₃AlF₆, and the solid products of the first two decomposition reactions are NH₄AlF₄ and AlF₃(NH₄F)_0.69, respectively. The three reactions occur at 194.9, 222.5 and 258.4 °C, respectively. Gibbs free energy changes of pertinent materials at the reaction temperatures were calculated. Enthalpy and entropy changes of the three reactions were analyzed by DSC method. Anhydrous aluminum fluoride was prepared. The XRD analysis and mass loss calculation show that AlF₃ with high purity can be obtained by heating (NH₄)₃AlF₆ at 400 °C for 3 h.

Key words: ammonium hexafluoroaluminate; thermal decomposition; aluminum fluoride; thermodynamic data